Printing blankets are used for direct, in-line coating in lithographic printing processes equipped with coating towers or coating units to apply gloss and/or matte overcoats at various levels on a variety of substrates, including corrugated stock, plain board, paper, film, foil, and laminates. The coating apparatus is used to apply these coatings principally in three situations: (i) when the entire substrate is to be coated; (ii) when the entire substrate is to be coated with the exception of certain areas where the coating will interfere with the adhesion of glue, printed labels, stamps, bar codes, or other such markings; and (iii) when certain, selected areas of the substrate are to be coated. The processes performed in situation (ii) are commonly referred to in the industry as "knock out" coating processes, whereas those performed in situation (iii) are commonly referred to spot coating processes.
One current practice in the industry in situation (ii) is to transfer an image to be printed directly onto a metal plate and mount a transparent printing blanket consisting of a polymeric support layer and a non-strippable polymer directly onto the plate using a suitable adhesive. Once mounted, the pressman uses a hand-held knife to carefully cut through the blanket, and then removes the entirety thereof (i.e., both the cured polymer and support) from the plate in portions thereof which are not to receive the coating. The plate/blanket composite which ultimately is produced then is mounted onto the plate cylinder of the coating apparatus, and is used to transfer coating to a printing blanket (mounted on a blanket cylinder) which, ultimately, transfers the coating to the substrate.
Another current practice in situation (ii), which avoids use and preparation of the printing cylinder, is to use rubber offset printing blankets as strippable coating blankets on the printing cylinder. These printing blankets typically consist of an opaque rubber printing layer disposed upon an opaque fabric support. Such a blanket is stretched slightly, mounted on a press, and an image corresponding to that ultimately to be coated is outlined with ink on the rubber surface using a lithographic printing plate. The pressman then uses a hand-held razor knife to carefully cut through the rubber surface of the blanket without penetrating through and damaging the support. The pressman then hand strips the cut rubber areas off the blanket. This requires a high skill level and that the press be stopped for, on average, about 45 minutes. If the support is pierced with the razor knife, the blanket typically is removed and the process started over. The "stripped" coating blanket which ultimately is produced is not reusable, as its fabric layer relaxes slightly upon removal from the press. Thus, the stripping process must be repeated for each, individual coating job.
Given these considerations, it is clear that any product which would allow a stripped coating blanket to be prepared off-line (thus sparing valuable press time), would allow for easy cutting and stripping of the printing surface, and/or would allow for reuse of the blanket thus prepared would yield significant advantages in terms of cost, convenience, and coating quality. The apparent need for such a product, however, still remains unfilled.